This invention relates generally as indicated to a bottom discharge drainmast for an aircraft and, more particularly, to a bottom discharge drainmast having at least one recirculating zone for capturing liquid which escapes from a release zone and redirecting the liquid into an appropriate flow path away from the drainmast.
A drainmast is used to eject waste liquid (e.g., water, discarded beverages, condensation, rain, etc.) from a moving aircraft. A drainmast typically comprises a fairing having a top mounting flange for attachment to the aircraft and an aerodynamically advantageous mast extending downward therefrom. A drain tube inside the fairing will usually include a top inlet end adapted for connection to an exit line of the aircraft""s waste water system and an outlet positioned to release liquid in an appropriate discharge direction.
Of particular relevance to the present invention is a bottom discharge drainmast. In such a drainmast, the outlet end of the drain tube is positioned at the bottom of the fairing and so that the discharge direction will be non-parallel with the airflow direction. For example, the drain tube may be shaped and positioned so that the discharge direction is at a downward angle (e.g., 45xc2x0 to 90xc2x0, 45xc2x0 to 75xc2x0, 45xc2x0 to 60xc2x0) relative to the expected airflow direction.
In a bottom discharge drainmast, the bottom portion, or cap, of the fairing will usually have a lower surface defining a liquid-release zone. The release zone is shaped to encourage the airflow to sweep as much as possible of the released liquid away from the fairing. The remaining liquid flows onto the outer surface of the drainmast and, if this liquid is not channeled away and/or if the drainmast surface is not sufficiently heated, ice will undesirably accumulate on the drainmast. Fins are often provided to channel the liquid to the back off of the aft end of the drain mast and heaters are provided to heat to prevent the formation of ice. Fins, by virtue of their protruding and/or high surface area geometry, are difficult to heat and require high heat density. This high heat density sometimes shortens the life of the drainmast and/or limits the materials which may be used to construct the drainmast.
The present invention provides an improved design for a bottom discharge drainmast which encourages a greater percentage of the released liquid to flow away from the drainmast in a primary flow path without the use of fins. With less water on the surface of the drainmast and no fins exposed to the surroundings, less heat will be required to prevent the formation of ice on the drainmast. With lower levels of heat being used, the drainmast is likely to last longer and a wider variety of materials, such as composites and silicon can be used to construct the drainmast.
More particularly, the present invention provides a drainmast comprising a fairing and a drain tube within the fairing. The fairing includes a flow-controlling cap having a lower surface defining an aft airflow-redirecting zone, a liquid-release zone forward of the airflow-redirecting zone, and a fore liquid-recirculation zone. The redirecting zone is shaped to redirect the airflow into the release zone in a direction parallel to the discharge direction. The release zone is shaped to encourage the redirected airflow to sweep a substantial portion of the released liquid away from the fairing in a primary flow path. The recirculation zone is shaped to capture escaped liquid from the release zone and to recirculate the escaped liquid back into the release zone.
The lower surface of the flow-controlling cap may include an aft concave portion defining the airflow redirecting zone, a fore convex portion defining the liquid-recirculating zone, and a transition portion therebetween defining the liquid-release zone. The aft portion may have a convex shape when viewed from the side and a half-oval shape when viewed from the bottom. The fore portion may have a concave shape when viewed from the side and a parabola shape when viewed from the bottom. The transition portion may have a trapezoid shape when viewed from the side and a roughly rectangular shape when viewed from the bottom.
The flow-controlling portion may have rear and side surfaces defining a second recirculation zone which is shaped to capture liquid which escapes from the primary flow path upstream of the recirculation zone and/or liquid which escapes from the first recirculation zone. This second recirculation zone may be shaped to direct the captured liquid into a secondary flow path, into the primary flow path, and/or into the first recirculation zone and may comprise a continuous groove positioned parallel to the expected airflow direction.
These and other features of the invention are fully described and particularly pointed out in the claims. The following descriptive annexed drawings set forth in detail a certain illustrative embodiment of the invention, this embodiment being indicative of but one of the various ways in which the principles of the invention may be employed.